Method for forming silicon nitride film selectively on sidewalls of trenches

ABSTRACT

A method for fabricating a layer structure in a trench includes: simultaneously forming a dielectric film containing a Si—N bond on an upper surface, and a bottom surface and sidewalls of the trench, wherein a top/bottom portion of the film formed on the upper surface and the bottom surface and a sidewall portion of the film formed on the sidewalls are given different chemical resistance properties by bombardment of a plasma excited by applying voltage between two electrodes between which the substrate is place in parallel to the two electrodes; and substantially removing the sidewall portion of the film by wet etching which removes the sidewall portion of the film more predominantly than the top/bottom portion according to the different chemical resistance properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/592,730, filed May 11, 2017, which is a continuation-in-part of U.S.patent application Ser. No. 15/048,422, filed Feb. 19, 2016, now issuedU.S. Pat. No. 9,754,779, each disclosure of which is herein incorporatedby reference in its entirety. The applicant/inventors herein explicitlyrescind and retract any prior disclaimers or disavowals made in anyparent, child or related prosecution history with regard to any subjectmatter supported by the present application.

BACKGROUND Field of the Invention

The present invention relates generally to a method for fabricating alayer structure constituted by a dielectric film containing a Si—N bondin a trench formed in an upper surface of a substrate.

Related Art

In manufacturing processes of large-scale integrated circuits (LSIs),there are several processes for forming sidewalls in trenches. Thesidewalls are used as spacers or used for blocking etching of astructure from side surfaces of trenches. Conventionally, the sidewallswere formed by forming a conformal film on surfaces of trenches, andthen removing portions thereof formed on an upper surface in which thetrenches were formed and portions formed on bottom surfaces of thetrenches by asymmetrical etching. However, when such a formation methodis used, over-etching is required in order to remove footing ofsidewalls in which the thickness of the sidewalls increases near and atthe bottom, forming a slope. Over-etching causes etching of anunderlying layer and causes damage to a layer structure.

Any discussion of problems and solutions in relation to the related arthas been included in this disclosure solely for the purposes ofproviding a context for the present invention, and should not be takenas an admission that any or all of the discussion was known at the timethe invention was made.

SUMMARY

In some embodiments, a film formed on a top surface of a substrate inwhich a trench is formed and on a bottom surface of the trench and afilm formed on the sidewalls of the trench possess different filmproperties associated with wet etching (i.e., directional control offilm properties). By subjecting the substrate to wet etching, it ispossible to remove selectively either the film formed on the top/bottomsurface of the trench or the film formed on the sidewalls of the trench,i.e., selectively forming either a film extending in a horizontaldirection or a film extending in a vertical direction in a trenchstructure. According to the above method, a horizontal or vertical layerin a trench structure can selectively be formed solely by wet etchingwithout dry etching as an etching means (i.e., directional control offilm formation).

In some embodiments, the film having directionally controlled filmproperties can be a silicon nitride film deposited by plasma-enhancedchemical vapor deposition (PECVD) or plasma-enhanced atomic layerdeposition (PEALD). Alternatively, in some embodiments, a siliconnitride film is deposited without directional control, and then the filmis treated to provide directionality of film properties. That is, whenion bombardment is exerted on a silicon nitride film during depositionof the film or after the deposition of the film, impurities can beremoved from the film, thereby causing densification of the film andimproving the film quality; however, when ion bombardment is intensifiedand asymmetrically exerted on the dielectric film in a directionperpendicular to the film, the film quality is degraded, therebydissociating Si—N bonds, decreasing the density of the film, andincreasing wet etching rates. The above phenomena are totally unexpectedsince generally ion bombardment is believed to cause densification of afilm and to decrease the wet etch rate. The intensity of ion bombardmentcan be directionally controlled by a plasma generated using a parallelplate electrode configuration, e.g., a capacitively coupled plasma,which can control the incident direction of ions, the dose of ions, andthe energy of ions. Based on the above principle which is not intendedto limit the invention, the directionality of film properties can becontrolled.

For purposes of summarizing aspects of the invention and the advantagesachieved over the related art, certain objects and advantages of theinvention are described in this disclosure. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings are greatlysimplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomiclayer deposition) apparatus for depositing a protective film usable inan embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supplysystem using a flow-pass system (FPS) usable in an embodiment of thepresent invention.

FIG. 2 is a flowchart illustrating steps of fabricating a layerstructure according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating steps of fabricating a layerstructure according to another embodiment of the present invention.

FIG. 4 is a flowchart illustrating steps of fabricating a layerstructure according to still another embodiment of the presentinvention.

FIG. 5 is a flowchart illustrating steps of fabricating a layerstructure according to yet another embodiment of the present invention.

FIG. 6 is a flowchart illustrating steps of fabricating a layerstructure according to a different embodiment of the present invention.

FIG. 7 is a graph showing the relationship between RF power and wet etchrate of a film formed on a top surface and that of a film formed onsidewalls of a trench, showing a threshold (reference) RF power,according to an embodiment of the present invention.

FIG. 8 shows Scanning Electron Microscope (SEM) photographs ofcross-sectional views of silicon nitride films formed according toembodiments of the present invention.

FIG. 9 shows a Scanning Electron Microscope (SEM) photograph of across-sectional view of a silicon nitride film formed according to anembodiment of the present invention.

FIG. 10 illustrates a cross-sectional view of a silicon nitride filmformed according to an embodiment of the present invention.

FIG. 11 illustrates a cross-sectional view of a silicon nitride filmformed according to another embodiment of the present invention.

FIG. 12 is a graph showing the relationship between RF power and Si—Npeak intensity [au] of a SiN film according to an embodiment of thepresent invention.

FIG. 13 is a graph showing the relationship between RF power and density[g/cm³] of a SiN film according to an embodiment of the presentinvention.

FIG. 14 is a graph showing a general relationship between plasma densityand wet etch rate of a film formed on a top surface and that of a filmformed on sidewalls of a trench according to an embodiment of thepresent invention.

FIG. 15 shows Scanning Electron Microscope (SEM) photographs ofcross-sectional views of silicon nitride films formed according toembodiments of the present invention.

FIG. 16 shows Scanning Electron Microscope (SEM) photographs ofcross-sectional views of silicon nitride films formed according to otherembodiments of the present invention.

FIG. 17 shows Scanning Electron Microscope (SEM) photographs ofcross-sectional views of silicon nitride films formed according to stillother embodiments of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid andmay be constituted by a single gas or a mixture of gases. In thisdisclosure, a process gas introduced to a reaction chamber through ashowerhead may be comprised of, consist essentially of, or consist of aprecursor gas and an additive gas. The precursor gas and the additivegas are typically introduced as a mixed gas or separately to a reactionspace. The precursor gas can be introduced with a carrier gas such as anoble gas. The additive gas may be comprised of, consist essentially of,or consist of a reactant gas and a dilution gas such as a noble gas. Thereactant gas and the dilution gas may be introduced as a mixed gas orseparately to the reaction space. A precursor may be comprised of two ormore precursors, and a reactant gas may be comprised of two or morereactant gases. The precursor is a gas chemisorbed on a substrate andtypically containing a metalloid or metal element which constitutes amain structure of a matrix of a dielectric film, and the reactant gasfor deposition is a gas reacting with the precursor chemisorbed on asubstrate when the gas is excited to fix an atomic layer or monolayer onthe substrate. “Chemisorption” refers to chemical saturation adsorption.A gas other than the process gas, i.e., a gas introduced without passingthrough the showerhead, may be used for, e.g., sealing the reactionspace, which includes a seal gas such as a noble gas. In someembodiments, “film” refers to a layer continuously extending in adirection perpendicular to a thickness direction substantially withoutpinholes to cover an entire target or concerned surface, or simply alayer covering a target or concerned surface. In some embodiments,“layer” refers to a structure having a certain thickness formed on asurface or a synonym of film or a non-film structure. A film or layermay be constituted by a discrete single film or layer having certaincharacteristics or multiple films or layers, and a boundary betweenadjacent films or layers may or may not be clear and may be establishedbased on physical, chemical, and/or any other characteristics, formationprocesses or sequence, and/or functions or purposes of the adjacentfilms or layers.

In this disclosure, “containing a Si—N bond” may refer to beingcharacterized by a Si—N bond or Si—N bonds, having a main skeletonsubstantially constituted by a Si—N bond or Si—N bonds, and/or having asubstituent substantially constituted by a Si—N bond or Si—N bonds. Adielectric film containing a Si—N bond includes, but is not limited to,a SiN film and a SiON film, which have a dielectric constant of about 2to 10, typically about 4 to 8.

In this disclosure, “annealing” refers to a process during which amaterial is treated to get into its stable form, e.g., a terminal group(such as an alcohol group and hydroxyl group) present in a component isreplaced with a more stable group (such as a Si-Me group) and/or forms amore stable form (such as a Si—O bond), typically causing densificationof a film.

Further, in this disclosure, the article “a” or “an” refers to a speciesor a genus including multiple species unless specified otherwise. Theterms “constituted by” and “having” refer independently to “typically orbroadly comprising,” “comprising,” “consisting essentially of,” or“consisting of” in some embodiments. Also, in this disclosure, anydefined meanings do not necessarily exclude ordinary and customarymeanings in some embodiments.

Additionally, in this disclosure, any two numbers of a variable canconstitute a workable range of the variable as the workable range can bedetermined based on routine work, and any ranges indicated may includeor exclude the endpoints. Additionally, any values of variablesindicated (regardless of whether they are indicated with “about” or not)may refer to precise values or approximate values and includeequivalents, and may refer to average, median, representative, majority,etc. in some embodiments.

In the present disclosure where conditions and/or structures are notspecified, the skilled artisan in the art can readily provide suchconditions and/or structures, in view of the present disclosure, as amatter of routine experimentation. In all of the disclosed embodiments,any element used in an embodiment can be replaced with any elementsequivalent thereto, including those explicitly, necessarily, orinherently disclosed herein, for the intended purposes. Further, thepresent invention can equally be applied to apparatuses and methods.

The embodiments will be explained with respect to preferred embodiments.However, the present invention is not limited to the preferredembodiments.

Some embodiments provide a method for fabricating a layer structureconstituted by a dielectric film containing a Si—N bond in a trenchformed in an upper surface of a substrate, comprising: (i)simultaneously forming a dielectric film containing a Si—N bond on theupper surface, and a bottom surface and sidewalls of the trench, whereina top/bottom portion of the dielectric film formed on the upper surfaceand the bottom surface and a sidewall portion of the dielectric filmformed on the sidewalls are given different chemical resistanceproperties by bombardment of a plasma excited by applying voltagebetween two electrodes between which the substrate is place in parallelto the two electrodes; and (ii) substantially removing either one of butnot both of the top/bottom portion and the sidewall portion of thedielectric film by wet etching which removes the one of the top/bottomportion and the sidewall portion of the dielectric film morepredominantly than the other according to the different chemicalresistance properties. The term “simultaneously forming” may refer toforming generally or substantially at the same time, in the sameprocess, or in the same step, which includes depositing generally orsubstantially at the same time, in the same process, or in the samestep, and/or treating generally or substantially at the same time, inthe same process, or in the same step. In this disclosure, the term“substantial” or “substantially” may refer to ample, considerable, ormaterial quantity, size, time, or space (e.g., at least 70%, 80%, 90%,or 95% relative to the total or referenced value) recognized by askilled artisan in the art to be sufficient for the intended purposes orfunctions.

FIG. 2 is a flowchart illustrating steps of fabricating a layerstructure according to an embodiment of the present invention. Step S1and step S2 correspond to steps (i) and (ii), respectively. In step S1,by using plasma bombardment, a dielectric film having directionality offilm properties is formed over a trench. The plasma bombardment can beapplied during the deposition of the film or after the completion ofdeposition of the film. In step S2, according to the difference in thefilm properties between the top/bottom portion of the film and thesidewall portion of the film, one of the portions of the film is morepredominantly etched than the other by wet etching, leaving only one ofthe portions in the layer structure.

In step S2, the wet etching is conducted using a solution of hydrogenfluoride (HF), for example.

By adjusting bombardment of a plasma excited by applying voltage betweentwo electrodes between which the substrate is place in parallel to thetwo electrodes, a top/bottom portion of the dielectric film formed onthe upper surface and the bottom surface and a sidewall portion of thedielectric film formed on the sidewalls can be given different chemicalresistance properties. A plasma is a partially ionized gas with highfree electron content (about 50%), and when a plasma is excited byapplying AC voltage between parallel electrodes, ions are accelerated bya self dc bias (V_(DC)) developed between plasma sheath and the lowerelectrode and bombard a film on a substrate placed on the lowerelectrode in a direction perpendicular to the film (the ion incidentdirection). The bombardment of a plasma can be represented by plasmadensity or kinetic energy of ions (ion energy). The plasma density canbe modulated mainly by tuning the pressure and RF power (the lower thepressure and the higher the power, the higher the plasma densitybecomes). The plasma density can also be modulated by applying a dc biasvoltage or an AC voltage with a lower frequency set for ions to follow(<1 MHz). The plasma density can be determined using a probe method(e.g., “High accuracy plasma density measurement using hybrid Langmuirprobe and microwave interferometer method,” Deline C, et al., Rev. Sci.Instrum. 2007 November; 78(11): 113504, the disclosure of which isincorporated by reference in its entirety). When inserting a probe in aplasma and applying a voltage thereto, an electric current flows throughthe probe, which is called “ion saturation current” (I_(i)) which can becalculated as follows, and then the plasma density (N_(p)) can becalculated as follows:

I_(i)=e×N_(e)√(kT_(e)/M)×exp(½)eA; N_(p)=I_(i)√(M/kT_(e))/exp(½)eA,wherein I_(i): ion saturation current [A]; A: surface area of the probe[m²]; e: electronic charge [C]; Ne: electron density [m⁻³]; k:Boltzmann's constant [J/K]; T_(e): electron temperature [K]; M: ion mass[kg].

FIG. 14 is a graph showing a general relationship between plasma densityand wet etch rate of a film formed on a top surface and that of a filmformed on sidewalls of a trench according to an embodiment of thepresent invention. In this graph, the chemical resistance properties arerepresented by wet etch rate. On the top/bottom surface of the film,plasma bombardment is exerted generally in a direction perpendicular tothe film surface, whereas on the sidewall surface of the film, plasmabombardment is exerted generally in a direction parallel to the filmsurface. The wet etch rate of a film formed on the top/bottom surfacesof a trench is low when the plasma density is low since ions included inthe plasma exerted on the film remove impurities and cause densificationof the film. However, the wet etch rate of the film formed on thetop/bottom surfaces increases as the plasma density increases as shownin FIG. 14, because the dose of ions is so high as to enhancedissociation of Si—N bond. On the other hand, the wet etch rate of afilm formed on the sidewall surfaces of the trench is high when theplasma density is low since the dose of ions included in the plasmaexerted on the film is insufficient to remove impurities and to causedensification of the film. However, the wet etch rate of the film formedon the sidewall surfaces decreases as the plasma density increases asshown in FIG. 14. In other words, the film quality of the film formed onthe top/bottom surfaces is degraded as the plasma density increases,whereas the film quality of the film formed on the sidewall surface isimproved as the plasma density increases. Thus, there is a thresholdpoint in the plasma density where the film quality (or filmcharacteristics) of the film on the top/bottom surfaces and that of thefilm on the sidewall are substantially equivalent, i.e., the lineshowing the relationship between plasma density and the wet etch rate ofthe film formed on the top/bottom surfaces and that of the film formedon the sidewalls intersect at the threshold point as shown in FIG. 14.The film characteristics of the film on the top/bottom surfaces and thatof the film on the sidewall surface are reversed at the threshold point.Accordingly, by adjusting the plasma density, the film havingdirectionality of film properties can be formed. When the plasma densityis set to be lower than the threshold point, the film on the sidewallscan be more predominantly removed than is the film on the top/bottomsurfaces by wet etching, whereas when the plasma density is set to behigher than the threshold point, the film on the top/bottom surfaces canbe more predominantly removed than is the film on the sidewalls by wetetching. Accordingly, a desired layer structure can be fabricated.

In FIG. 14, the intersecting point (threshold point) is changedaccording to the duration of application of voltage, the frequency, thepressure, the distance between the electrodes, the temperature, etc.,wherein, generally, the longer the duration of application of voltage,and the lower the pressure, the lower the plasma density at theintersecting point becomes. It should be noted that when the pressure,RF power, voltage, etc. are constant, a relationship substantiallysimilar to that shown in FIG. 14 can be obtained between wet etch rateand RF power between parallel electrodes. The threshold point can bedetermined prior to steps (i) and (ii) based on this disclosure androutine experimentation. Thus, in some embodiments, the method forfabricating a layer structure further comprises, prior to steps (i) and(ii), repeating the following steps to determine the threshold point(reference point): (a) simultaneously forming a dielectric film underthe same conditions as in step (i) except that the voltage is changed asa variable; and (b) substantially removing either one of but not both ofthe top/bottom portion and the sidewall portion of the dielectric filmby wet etching under the same conditions as in step (ii).

FIG. 3 is a flowchart illustrating steps of fabricating a layerstructure according to an embodiment of the present invention. Step S11corresponds to steps (a) and (b), and steps S12 and S13 correspond tosteps (i) and (ii), respectively. In step S11, the threshold voltage forplasma bombardment for reversing film characteristics of a top/bottomportion and a sidewall portion of a film is determined. In step S12, byusing plasma bombardment at a voltage adjusted with reference to thedetermined threshold voltage, a dielectric film having directionality offilm properties is formed over a trench. For example, when a voltagehigher than the threshold voltage is applied between the electrodes instep S12, the wet etch rate of the top/bottom portion of the filmbecomes higher than that of the sidewall portion of the film, resultingin predominantly removing the top/bottom portion of the film, ratherthan the sidewall portion of the film by wet etching in step S13. On theother hand, when a voltage lower than the threshold voltage is appliedbetween the electrodes in step S12, the wet etch rate of the sidewallportion of the film becomes higher than that of the top/bottom portionof the film, resulting in predominantly removing the sidewall portion ofthe film, rather than the top/bottom portion of the film by wet etchingin step S13.

When ion bombardment is exerted on a film without using a parallelelectrode configuration, e.g., by using a reactant in low-pressurechemical vapor deposition (LPCVD), a threshold point such as that shownin FIG. 14 would not be obtained since the reactant in LPCVD does notcreate asymmetrical ion bombardment, i.e., does not createdirectionality of film properties. For example, U.S. Publication No.2003/0029839 discloses LPCVD in which nitrogen-containing ions such asN₂ ⁺ are implanted to form a nitrogen-enriched layer, followed bythermal annealing to promote Si—N and N—H bonds in the layer so as toreduce the wet etch rate of the layer. In contrast, in some embodimentsof the present invention, asymmetrical plasma bombardment using nitrogenis exerted on a top/bottom layer, which does not enrich nitrogen in thelayer, but dissociates Si—N bonds and reduces the density of the layer,thereby increasing the wet etch rate of the layer formed on thetop/bottom surfaces, relative to the wet etch rate of the layer formedon the sidewalls of a trench. In the above, when Si—N bonds aredissociated, Si dangling bonds and N dangling bonds are formed, whichare ultimately terminated by hydrogen, forming N—H bonds and Si—H bonds.As a result of dissociating Si—N bonds, the density of the layer isdecreased, and the wet etch rate is increased. Thus, in someembodiments, no thermal annealing (such as at 900° C.) is conductedbetween steps (i) and (ii) in order to avoid densification of thetop/bottom layer (i.e., to avoid reducing the wet etch rate of thetop/bottom layer). Further, in some embodiments, the incident energy ofions is less than approximately 200 eV (plasma potential isapproximately 100 to 200 V), which is lower than that disclosed in U.S.Publication No. 2003/0029839 (0.5 to 20 keV). As with the reactant inLPCVD, a reactant in thermal atomic layer deposition (ALD) and a plasmaof remote plasma deposition do not form a threshold point such as thatshown in FIG. 14 since the plasmas of thermal ALD and remote plasmadeposition also do not create asymmetrical ion bombardment, i.e., do notcreate directionality of film properties. Further, when a plasma such assurface wave plasma (SWP) having low electron temperature and low ionkinetic energy of incident ions is used, the effect of ion bombardmentis very limited, and thus, film degradation does not occur, and thus, itis difficult to create directionality of film properties. Furthermore,even when plasma bombardment is exerted on a film constituted by siliconoxide, the film quality of the silicon oxide film is not degraded, andthus, it is difficult to create directionality of film properties.

In some embodiments, the plasma is a capacitively coupled plasma (CCP)which is excited by applying RF power to one of the two electrodes.Further, in some embodiments, inductively coupled plasma (ICP), electroncyclotron resonance (ECR) plasma, microwave surface wave plasma, heliconwave plasma, etc. can be used as the plasma, wherein bias voltage isapplied to the electrodes as necessary to increase dc bias voltagebetween the plasma and electrode.

In some embodiments, the RF power is higher than the reference RF powerat which the chemical resistance properties of the top/bottom portion ofthe dielectric film and the sidewall portion of the dielectric film aresubstantially equivalent, wherein the wet etching removes the top/bottomportion of the dielectric film selectively relative to the sidewallportion of the dielectric film.

In some embodiments, the plasma is a plasma of Ar, N₂, and/or O₂ orother atoms which have an atomic number higher than hydrogen or helium.

In some embodiments, the trench has a width of 10 to 50 nm (typically 15to 30 nm) (wherein when the trench has a length substantially the sameas the width, it is referred to as a hole/via, and a diameter thereof is10 to 50 nm), a depth of 30 to 200 nm (typically 50 to 150 nm), and anaspect ratio of 3 to 20 (typically 3 to 10).

In some embodiments, the dielectric film can be used as an etchingstopper, low-k spacer, or gap-filler. For example, when only thesidewall portion is left, the portion can be used as a spacer forspacer-defined double patterning (SDDP), or when only the top/bottomportion is left, the portion can be used as a mask used for solid-statedoping (SSD) of a sidewall layer exclusively.

In some embodiments, step (i) comprises: (ia) placing a substrate havinga trench in its upper surface between the electrodes; and (ib)depositing the dielectric film on the substrate by plasma-enhancedatomic layer deposition (PEALD) using nitrogen gas as a reactant gas,wherein the plasma is a capacitively coupled plasma (CCP) which isexcited by applying RF power to one of the two electrodes in each cycleof the PEALD, wherein the RF power is higher than the reference RF powerat which the chemical resistance properties of the top/bottom portion ofthe dielectric film and the sidewall portion of the dielectric film aresubstantially equivalent so that the wet etching in step (ii) removesthe top/bottom portion of the dielectric film selectively relative tothe sidewall portion of the dielectric film. In the above, the filmhaving directionality of film properties is formed as the film isdepositing, not after the completion of deposition of the film.

FIG. 4 is a flowchart illustrating steps of fabricating a layerstructure according to still another embodiment of the presentinvention. Step S21 corresponds to step (ib), and step S22 correspondsto step (ii). In step S21, a dielectric film having directionality offilm properties is deposited over a trench by using plasma bombardmentat a voltage higher than the threshold voltage, and in step S22, atop/bottom portion of the film is more predominantly removed than is asidewall portion of the film, so that substantially only the sidewallportion is left in the layer structure.

In some embodiments, step (i) comprises: (ia) placing a substrate havinga trench on its upper surface between the electrodes; and (ic)depositing the dielectric film on the substrate by plasma-enhancedatomic layer deposition (PEALD) using nitrogen gas as a reactant gas,wherein the plasma is a capacitively coupled plasma (CCP) which isexcited by applying RF power to one of the two electrodes in each cycleof the PEALD, wherein the RF power is lower than reference RF power atwhich the chemical resistance properties of the top/bottom portion ofthe dielectric film and the sidewall portion of the dielectric film aresubstantially equivalent so that the wet etching in step (ii) removesthe sidewall portion of the dielectric film selectively relative to thetop/bottom portion of the dielectric film. In the above, the film havingdirectionality of film properties is formed as the film is depositing,not after the completion of deposition of the film.

FIG. 5 is a flowchart illustrating steps of fabricating a layerstructure according to yet another embodiment of the present invention.Step S31 corresponds to step (ic), and step S32 corresponds to step(ii). In step S31, a dielectric film having directionality of filmproperties is deposited over a trench by using plasma bombardment at avoltage lower than the threshold voltage, and in step S32, a sidewallportion of the film is more predominantly removed than is a top/bottomportion of the film, so that substantially only the top/bottom portionis left in the layer structure.

In some embodiments, the dielectric film is SiN film or SiON film orother Si—N bond-containing film.

In some embodiments, the PEALD or other deposition methods uses one ormore compounds selected from the group consisting of aminosilane,halogenated silane, monosilane, and disilane as a precursor. Theaminosilane and halogenated silane include, but are not limited to,Si₂Cl₆, SiCl₂H₂, SiI₂H₂, bisdiethylaminosilane, bisdimethylaminosilane,hexaethylaminodisilane, tetraethylaminosilane, tart-butylaminosilane,bistart-butylaminosilane, trimehylsilyldiethylamine,trimethysilyldiethylamine, and bisdimethylaminodimethylsilane.

In some embodiments, step (i) comprises: (iA) depositing a dielectricfilm on a substrate having a trench in its upper surface; (iB) placingthe substrate between the two electrodes; and (iC) exciting the plasmabetween the electrodes to treat a surface of the deposited dielectricfilm without depositing a film, wherein the plasma is a capacitivelycoupled plasma (CCP) which is excited by applying RF power to one of thetwo electrodes, wherein the RF power is higher than the reference RFpower at which the chemical resistance properties of the top/bottomportion of the dielectric film and the sidewall portion of thedielectric film are substantially equivalent so that the wet etching instep (ii) removes the top/bottom portion of the dielectric filmselectively relative to the sidewall portion of the dielectric film. Inthe above, the film having directionality of film properties is formedafter completion of deposition of a film, by treating the film. In theabove, step (ii) is post-deposition treatment which need not be cyclic.

FIG. 6 is a flowchart illustrating steps of fabricating a layerstructure according to a different embodiment of the present invention.Step S41 corresponds to step (iA), step S42 corresponds to steps (iB)and (iC), and step S43 corresponds to step (ii). In step S41, adielectric film is deposited over a trench, which film need not havedirectionality of film properties, although it can already possessdirectionality of film properties. In step S42, plasma bombardment aspost-deposition treatment is exerted on the film at a voltage higherthan the threshold voltage so that the wet etch rate of a top/bottomportion of the film is higher than that of a sidewall portion of thefilm. In step S43, the top/bottom portion of the film is morepredominantly removed than is the sidewall portion of the film by wetetching, so that substantially only the sidewall portion of the film isleft in the layer structure. Since the film is already deposited beforethe post-deposition treatment, the use of a voltage lower than thethreshold voltage may not be effective because the wet etch rate of thesidewall portion does not become higher than that of the as-depositedfilm by exerting plasma bombardment on the film as illustrated in FIG.14 discussed above.

In some embodiments, the deposited dielectric film has a thickness ofapproximately 10 nm or less (typically approximately 5 nm or less). Ifthe film to be treated is thicker than approximately 10 nm, plasmabombardment does not reach a bottom of the film, i.e., it is difficultto adjust the wet etch rate of the film entirely in the thicknessdirection.

The dielectric film subjected to the post-deposition treatment can bedeposited on the substrate by any suitable deposition methods includingplasma-enhanced atomic layer deposition (PEALD), thermal ALD,low-pressure chemical vapor deposition (LPCVD), remote plasmadeposition, PECVD, etc. Preferably, the dielectric film is deposited byALD since ALD can provide a high conformality such as more thanapproximately 70% (or more than 80% or 90%).

In some embodiments, no annealing is conducted after depositing thedielectric film and before step (ii).

In some embodiments, the plasma in step (i) is a capacitively coupledplasma (CCP) which is excited by applying RF power to one of the twoelectrodes, wherein plasma density is higher than reference plasmadensity at which the chemical resistance properties of the top/bottomportion of the dielectric film and the sidewall portion of thedielectric film are substantially equivalent, wherein the wet etching instep (ii) removes the top/bottom portion of the dielectric filmselectively relative to the sidewall portion of the dielectric film. Asdiscussed above in relation to FIG. 14, the wet etch rate of a filmformed on a top surface and that of a film formed on sidewalls of atrench can be adjusted by changing the plasma density, and the plasmadensity can be modulated mainly by tuning the pressure and/or RF power(the lower the pressure and/or the higher the power, the higher theplasma density becomes), and/or by applying RF power having a lowfrequency (<1 MHz).

In some embodiments, the plasma density is modulated by tuning thepressure in the reaction space, wherein the plasma density increases bylowering the pressure. In that case, the method further comprises, priorto steps (i) and (ii), repeating the following steps to determine thereference plasma density: (a) simultaneously forming a dielectric filmunder the same conditions as in step (i) except that the pressure ischanged as a variable; and (b) substantially removing either one of butnot both of the top/bottom portion and the sidewall portion of thedielectric film by wet etching under the same conditions as in step(ii).

In some embodiments, the pressure in step (i) is controlled below 350Pa, including 300 Pa, 250 Pa, 200 Pa, 150 Pa, 100 Pa, 50 Pa, and 10 Pa,and any values between any two of the foregoing values.

In some embodiments, the plasma density is modulated by tuning a ratioof high frequency RF power to low frequency RF power constituting the RFpower, wherein the plasma density increases by decreasing the ratio. Insome embodiments, the high frequency RF power has a frequency of 1 MHzor higher (e.g., 10 MHz to 60 MHz), and the low frequency RF power has afrequency of less than 1 MHz (e.g., 200 kHz to 800 kHz). In the above,the method further comprises, prior to steps (i) and (ii), repeating thefollowing steps to determine the reference plasma density: (a)simultaneously forming a dielectric film under the same conditions as instep (i) except that the ratio is changed as a variable; and (b)substantially removing either one of but not both of the top/bottomportion and the sidewall portion of the dielectric film by wet etchingunder the same conditions as in step (ii).

In some embodiments, the ratio of high frequency RF power (HRF) to lowfrequency RF power (LRF) is 0/100 to 95/5 (e.g., 10/90 to 90/10). Insome embodiments, the RF power consists of the low frequency RF power.In some embodiments, the total RF power is 100 W to 600 W for a 300-mmwafer (which power is applicable to any size of wafer as wattage perarea, i.e., 0.14 W/cm² to 0.85 W/cm²).

In some embodiments, any one or more of the variables discussed in thisdisclosure can be used to manipulate the plasma density when depositinga dielectric film so as to control selective etching in the etchingprocess.

In the above embodiments where the ratio of HRF/LRF is controlled, lowpressure and high RF power are not required as a variable to manipulatethe plasma density when depositing a dielectric film, thereby making theprocess conditions less restricted. Further, in the embodiments,abnormal discharge by applying high RF power can be avoided.

In other embodiments where the wet etching in step (ii) removes thesidewall portion of the dielectric film selectively relative to thetop/bottom portion of the dielectric film, plasma density is set lowerthan reference plasma density at which the chemical resistanceproperties of the top/bottom portion of the dielectric film and thesidewall portion of the dielectric film are substantially equivalent.

In some embodiments, the deposition cycle may be performed by PEALD, onecycle of which is conducted under conditions shown in Table 1 below.

TABLE 1 (numbers are approximate) Conditions for Deposition CycleSubstrate temperature 100 to 600° C. (preferably 250 to 550° C.)Pressure 10 to 2000 Pa (preferably 100 to 800 Pa); Less than 350 Pa(preferably 250 Pa or less) for WER of top/bottom being higher than WERof sidewall Precursor SiI₂H₂, etc. Precursor pulse 0.05 to 10 sec(preferably 0.2 to 1 sec) Precursor purge 0.05 to 10 sec (preferably 0.2to 3 sec) Reactant N₂ + H₂ mixture, or NH₃ + N₂ mixture Flow rate ofreactant 100 to 20000 sccm (preferably 1000 to 3000 sccm) for N₂;(continuous) 0 to 6000 sccm (preferably 0 to 600 sccm) for H₂ or NH₃(H₂/N₂ = 0-0.5, preferably 0-0.2) Flow rate of carrier gas 100 to 5000sccm (preferably 1000 to 3000 sccm) Ar or N₂ (continuous) Flow rate ofdilution gas 0 to 10000 sccm (preferably 0 to 5000 sccm) Ar or N₂(continuous) RF power (13.56 MHz) for a Less than 600 W (preferably 100to 500 W) for WER of 300-mm wafer sidewall being higher than WER oftop/bottom; 600 W or more (preferably 600 to 1000 W) for WER oftop/bottom being higher than WER of sidewall A ratio of HRF/LRF Over95/5 (typically 100/0) for WER of sidewall being higher than WER oftop/bottom; 0/100 to 95/5 (preferably 0/100 to 90/10) for WER oftop/bottom being higher than WER of sidewall RF power pulse 0.05 to 30sec (preferably 1 to 5 sec) Purge 0.05 to 10 sec (preferably 0.2 to 3sec) Growth rate per cycle (on top 0.02 to 0.06 nm/cycle surface) Stepcoverage (side/top; 20 to 100%; 30 to 100% (preferably, 50 to 100%; 50to side/bottom) 100%) Distance between electrodes 5 to 30 mm (preferably7 to 20 mm)

In some embodiments, the post-deposition treatment may be performedunder conditions shown in Table 2 below.

TABLE 2 (numbers are approximate) Conditions for Post-DepositionTreatment Thickness of SiN film 2 to 15 nm (preferably 5 to 10 nm)Substrate temperature 25 to 600° C. (preferably 100 to 500° C.) Pressure10 to 2000 Pa (preferably 100 to 500 Pa) Reactant N₂, H₂, NH₃ Flow rateof reactant 100 to 20000 sccm (preferably 1000 to 3000 sccm) for N₂;(continuous) 0 to 6000 sccm (preferably 0 to 600 sccm) for H₂ or NH₃(H₂/N₂ = 0-0.5, preferably 0-0.2) Flow rate of carrier gas 100 to 5000sccm (preferably 1000 to 3000 sccm) Ar or N₂ (continuous) Flow rate ofdilution gas 0 to 10000 sccm (preferably 0 to 5000 sccm) Ar or N₂(continuous) RF power (13.56 MHz) for a More than 600 W (preferably 600to 1000 W) 300-mm wafer Duration of RF power 1 to 600 sec. (preferably30 to 180 sec.) application Distance between electrodes 5 to 30 mm(preferably 7 to 20 mm)

In the above, although no precursor is fed to the reaction chamber, anda carrier gas flows continuously.

In some embodiments, wet etching may be performed under conditions shownin Table 3 below.

TABLE 3 (numbers are approximate) Conditions for Wet etching Etchingsolution HF 0.05-5% Etching solution temperature 10 to 50° C.(preferably 15 to 30° C.) Duration of etching 1 sec to 5 min (preferably1 to 3 min) Etching rate 0.1 to 5 nm/min (preferably 0.5 to 2 nm/min)

For wet etching, any suitable single-wafer type or batch type apparatusincluding any conventional apparatuses can be used. Also, any suitablesolution for wet etching including any conventional solutions, such asphosphoric acid, can be used.

In some embodiments, in place of wet etching, any other suitable etchingsuch as dry etching or plasma etching can be conducted. A skilledartisan can readily determine the etching conditions such astemperature, duration, etchant concentration, as routine experimentationin view of this disclosure.

In some embodiments, an insulation film can be formed only on a sidewallof a trench as follows:

1) forming a SiN film over a substrate having a trench pattern, in whicha pulse of feeding a precursor and a pulse of exposing the substrate toan ambient atmosphere containing nitrogen species excited by a plasmaare repeated, in which the plasma is excited in a manner exerting plasmabombardment on the substrate in a direction perpendicular to thesubstrate (the incident angle of ions is perpendicular to the substrate)under conditions such that the wet etch rate of a sidewall portion ofthe film is lower than that of a top/bottom portion of the film; and

2) removing the top/bottom portion of the film by wet etching.

In the above process sequence, the precursor is supplied in a pulseusing a carrier gas which is continuously supplied. This can beaccomplished using a flow-pass system (FPS) wherein a carrier gas lineis provided with a detour line having a precursor reservoir (bottle),and the main line and the detour line are switched, wherein when only acarrier gas is intended to be fed to a reaction chamber, the detour lineis closed, whereas when both the carrier gas and a precursor gas areintended to be fed to the reaction chamber, the main line is closed andthe carrier gas flows through the detour line and flows out from thebottle together with the precursor gas. In this way, the carrier gas cancontinuously flow into the reaction chamber, and can carry the precursorgas in pulses by switching the main line and the detour line. FIG. 1Billustrates a precursor supply system using a flow-pass system (FPS)according to an embodiment of the present invention (black valvesindicate that the valves are closed). As shown in (a) in FIG. 1B, whenfeeding a precursor to a reaction chamber (not shown), first, a carriergas such as Ar (or He) flows through a gas line with valves b and c, andthen enters a bottle (reservoir) 30. The carrier gas flows out from thebottle 30 while carrying a precursor gas in an amount corresponding to avapor pressure inside the bottle 30, and flows through a gas line withvalves f and e, and is then fed to the reaction chamber together withthe precursor. In the above, valves a and d are closed. When feedingonly the carrier gas (noble gas) to the reaction chamber, as shown in(b) in FIG. 1B, the carrier gas flows through the gas line with thevalve a while bypassing the bottle 30. In the above, valves b, c, d, e,and f are closed.

The precursor may be provided with the aid of a carrier gas. Since ALDis a self-limiting adsorption reaction process, the number of depositedprecursor molecules is determined by the number of reactive surfacesites and is independent of precursor exposure after saturation, and asupply of the precursor is such that the reactive surface sites aresaturated thereby per cycle. A plasma for deposition may be generated insitu, for example, in an ammonia gas that flows continuously throughoutthe deposition cycle. In other embodiments the plasma may be generatedremotely and provided to the reaction chamber.

As mentioned above, each pulse or phase of each deposition cycle ispreferably self-limiting. An excess of reactants is supplied in eachphase to saturate the susceptible structure surfaces. Surface saturationensures reactant occupation of all available reactive sites (subject,for example, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage. In some embodiments the pulse time ofone or more of the reactants can be reduced such that completesaturation is not achieved and less than a monolayer is adsorbed on thesubstrate surface.

The process cycle can be performed using any suitable apparatusincluding an apparatus illustrated in FIG. 1A, for example. FIG. 1A is aschematic view of a PEALD apparatus, desirably in conjunction withcontrols programmed to conduct the sequences described below, usable insome embodiments of the present invention. In this figure, by providinga pair of electrically conductive flat-plate electrodes 4, 2 in paralleland facing each other in the interior 11 (reaction zone) of a reactionchamber 3, applying HRF power (13.56 MHz or 27 MHz) 20 to one side, andelectrically grounding the other side 12, a plasma is excited betweenthe electrodes. A temperature regulator is provided in a lower stage 2(the lower electrode), and a temperature of a substrate 1 placed thereonis kept constant at a given temperature. The upper electrode 4 serves asa shower plate as well, and reactant gas (and noble gas) and precursorgas are introduced into the reaction chamber 3 through a gas line 21 anda gas line 22, respectively, and through the shower plate 4.Additionally, in the reaction chamber 3, a circular duct 13 with anexhaust line 7 is provided, through which gas in the interior 11 of thereaction chamber 3 is exhausted. Additionally, a dilution gas isintroduced into the reaction chamber 3 through a gas line 23. Further, atransfer chamber 5 disposed below the reaction chamber 3 is providedwith a seal gas line 24 to introduce seal gas into the interior 11 ofthe reaction chamber 3 via the interior 16 (transfer zone) of thetransfer chamber 5 wherein a separation plate 14 for separating thereaction zone and the transfer zone is provided (a gate valve throughwhich a wafer is transferred into or from the transfer chamber 5 isomitted from this figure). The transfer chamber is also provided with anexhaust line 6. In some embodiments, the deposition of multi-elementfilm and surface treatment are performed in the same reaction space, sothat all the steps can continuously be conducted without exposing thesubstrate to air or other oxygen-containing atmosphere. In someembodiments, a remote plasma unit can be used for exciting a gas.

In some embodiments, in the apparatus depicted in FIG. 1A, the system ofswitching flow of an inactive gas and flow of a precursor gasillustrated in FIG. 1B (described earlier) can be used to introduce theprecursor gas in pulses without substantially fluctuating pressure ofthe reaction chamber.

In some embodiments, a dual chamber reactor (two sections orcompartments for processing wafers disposed close to each other) can beused, wherein a reactant gas and a noble gas can be supplied through ashared line whereas a precursor gas is supplied through unshared lines.

A skilled artisan will appreciate that the apparatus includes one ormore controller(s) (not shown) programmed or otherwise configured tocause the deposition and reactor cleaning processes described elsewhereherein to be conducted. The controller(s) are communicated with thevarious power sources, heating systems, pumps, robotics, and gas flowcontrollers or valves of the reactor, as will be appreciated by theskilled artisan.

The present invention is further explained with reference to workingexamples below. However, the examples are not intended to limit thepresent invention. In the examples where conditions and/or structuresare not specified, the skilled artisan in the art can readily providesuch conditions and/or structures, in view of the present disclosure, asa matter of routine experimentation. Also, the numbers applied in thespecific examples can be modified by a range of at least ±50% in someembodiments, and the numbers are approximate.

In some embodiments, an insulation film can be formed only on a sidewallof a trench as follows:

1) forming a SiN film over a substrate having a trench pattern (the filmmay or may not have directionality of film properties);

2) treating the film with a plasma excited in a manner exerting plasmabombardment on the substrate in a direction perpendicular to thesubstrate (the incident angle of ions is perpendicular to the substrate)under conditions such that the wet etch rate of a sidewall portion ofthe film is lower than that of a top/bottom portion of the film; and

3) removing the top/bottom portion of the film by wet etching.

EXAMPLES Example 1

A SiN film was formed on a Si substrate (Φ300 mm) having trenches byPEALD, one cycle of which was conducted under the conditions shown inTable 4 (deposition cycle) below using the PEALD apparatus illustratedin FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B.

After taking out the substrate from the reaction chamber, the substratewas subjected to wet etching under the conditions shown in Table 4below.

TABLE 4 (numbers are approximate) Conditions for Deposition CycleSubstrate temperature 400° C. Pressure 350 Pa Precursor SiI₂H₂ Precursorpulse 0.3 sec Precursor purge 0.5 sec Reactant N₂ Flow rate of reactant(continuous) 2000 sccm Flow rate of carrier gas (continuous) 2000 sccmN₂ Flow rate of dilution gas (continuous) 0 sccm RF power (13.56 MHz)for a 300-mm wafer Variable (see FIG. 7) RF power pulse 3.3 sec Purge0.1 sec Growth rate per cycle (on top surface) 0.05 nm/cycle Number ofcycles (thickness of film on top 200 times (10 nm) surface) Stepcoverage (side/top; side/bottom) 100%; 100% Trench depth/width (nm)100/33 (AR = about 3) Distance between electrodes 15 mm Conditions forWet etching Etching solution 0.5% HF Etching solution temperature 20° C.Duration of etching 2 min Etching rate Variable (see FIG. 7)

The results are shown in FIG. 7. FIG. 7 is a graph showing therelationship between RF power and wet etch rate of the film formed onthe top surface and that of the film formed on the sidewalls of thetrench, showing a threshold (reference) RF power. As shown in FIG. 7,the wet etch rate of the sidewall portion decreased as RF powerincreased, whereas the wet etch rate of the top/bottom portionsincreased as the RF power increased, wherein the line representing theformer and the line representing the latter intersect at an RF power ofapproximately 600 W. That is, the threshold RF power was approximately600 W, and it can be understood that when RF power applied between theelectrodes is higher than approximately 600 W, the top/bottom portionsof the film can be removed selectively relative to the sidewall portionof the film, whereas when RF power applied between the electrodes islower than approximately 600 W, the sidewall portion of the film can beremoved selectively relative to the top/bottom portions of the film.

Further, prior to the wet etching, the top portion of the film wassubjected to additional analyses: Si—N peak intensity and density. FIG.12 is a graph showing the relationship between RF power and Si—N peakintensity [au] of the SiN film. FIG. 13 is a graph showing therelationship between RF power and density [g/cm³] of the SiN film. Ascan be seen from FIGS. 12 and 13, contrary to common technologicalknowledge (i.e., when increasing RF power, densification of the filmoccurs), asymmetrical plasma bombardment to the SiN film broke Si—Nbonds when RF power increased, and as a result of dissociation of Si—Nbonds, the density of the film decreased (the density is typically in arange of 2.6 to 3.2 g/cm³), wherein the density of a film portion to beremoved by wet etching is lower than that of a film portion to remainthrough wet etching).

Example 2

The SiN films were deposited under the conditions shown in Table 5,where the threshold RF power was determined to be approximately 400 W inthe same manner as in Example 1. The SiN films were then subjected towet etching under the conditions shown in Table 5. FIG. 8 shows ScanningTransmission Electron Microscope (STEM) photographs of cross-sectionalviews of the silicon nitride films. As can be seen from FIG. 8, when RFpower was 700 W, the top/bottom portions of the film were selectivelyremoved by wet etching, and substantially no film remained (no residualfilm was observed) on the top surface and at the bottom of the trench.When RF power was 500 W, the top/bottom portions of the film were morepredominantly removed than was the sidewall portion of the film by wetetching, but residual film remained on the top surface and at the bottomof the trench, whereas the sidewall portion of the film mostly remained.When RF power was 300 W, the sidewall portion of the film was morepredominantly removed than were the top/bottom portions of the film bywet etching, and no residual film remained in some areas of thesidewall, whereas the top/bottom portions of the film mostly remained.

TABLE 5 (numbers are approximate) Conditions for Deposition CycleSubstrate temperature 200° C. Pressure 350 Pa PrecursorBisdiethylaminosilane Precursor pulse 0.2 sec Precursor purge 3 secReactant N₂ Flow rate of reactant (continuous) 2000 sccm Flow rate ofcarrier gas (continuous) 2000 sccm Ar Flow rate of dilution gas(continuous) 0 sccm RF power (13.56 MHz) for a 300-mm wafer Variable(see FIG. 8) RF power pulse 3 sec Purge 0.1 sec Growth rate per cycle(on top surface) 0.02 nm/cycle Number of cycles (thickness of film ontop 500 times (10 nm) surface) Step coverage (side/top; side/bottom)30%; 30% Trench depth/width (nm) 100/33 (AR = about 3) Distance betweenelectrodes 13 mm Conditions for Wet etching Etching solution 0.05% HFEtching solution temperature 20° C. Duration of etching 4 min Etchingrate Variable (see FIG. 8)

Example 3

The SiN film was deposited in the same manner as in Example 1 exceptthat RF power was 880 W. The SiN film was then subjected to wet etchingunder the same conditions as in Example 1. FIG. 9 shows a ScanningTransmission Electron Microscope (STEM) photograph of a cross-sectionalview of the SiN film after the wet etching. As can be seen from FIG. 9,substantially no film remained (no residual film was observed) on thetop surface and at the bottom of the trench.

Example 4 (Prophetic Example)

A SiN film is formed on a Si substrate (Φ300 mm) having trenches byPEALD in the same manner as in Example 1 except that RF power is 600 W.Thereafter, in the same reactor, the film is treated with a plasma underthe conditions shown in Table 6 below, where RF power is 800 W which ishigher than the threshold RF power, thereby causing damage to the topsurface of the substrate and the bottom surface of the trench anddegrading the film quality. After taking out the substrate from thereaction chamber, the substrate is subjected to wet etching under theconditions shown in Table 6 below.

TABLE 6 (numbers are approximate) Conditions for Surface treatmentSubstrate temperature 400° C. Pressure 350 Pa Reactant N₂ Flow rate ofreactant (continuous) 2000 sccm Flow rate of carrier gas (continuous)2000 sccm Flow rate of dilution gas (continuous) 0 sccm RF power (13.56MHz) for a 300-mm wafer 880 W Duration of RF power application 60 secDistance between electrodes 15 mm Conditions for Wet etching Etchingsolution 0.5% HF Etching solution temperature 20° C. Duration of etching2 min Etching rate (top/sidewall) 6 nm/min, 0.2 nm/min

FIG. 10 illustrates a cross-sectional view of the silicon nitride film.Since a portion 52 of the film formed on a sidewall 51 of a trenchformed in a substrate 51 does not receive substantial plasmabombardment, the portion 52 maintains film properties and remains afterwet etching. In contrast, since a portion of the film formed on a topsurface 51 b and a portion of the film formed on a bottom surface 51 areceive plasma bombardment, the portions degrade film properties and areremoved after wet etching.

Example 5 (Prophetic Example)

A SiN film is formed on a Si substrate (Φ300 mm) having trenches byPEALD, one cycle of which is conducted under the conditions shown inTable 7 (deposition cycle) below using the PEALD apparatus illustratedin FIG. 1A and a gas supply system (FPS) illustrated in FIG. 1B.

After taking out the substrate from the reaction chamber, the substrateis subjected to wet etching under the conditions shown in Table 7 below.

TABLE 7 (the numbers are approximate) Conditions for Deposition CycleSubstrate temperature 400° C. Pressure 350 Pa Precursor SiI₂H₂ Precursorpulse 0.3 sec Precursor purge 0.5 sec Reactant N₂ Flow rate of reactant(continuous) 2000 sccm Flow rate of carrier gas (continuous) 2000 sccmN₂ Flow rate of dilution gas (continuous) 0 sccm RF power (13.56 MHz)for a 300-mm wafer 100 W RF power pulse 3.3 sec Purge 0.1 sec Growthrate per cycle (on top surface) 0.05 nm/cycle Number of cycles(thickness of film on top 200 times (10 nm) surface) Trench depth/width(nm) 100/33 (AR = about 3) Step coverage (side/top; side/bottom) 100%;100% Distance between electrodes 15 mm Conditions for Wet etchingEtching solution 0.5% HF Etching solution temperature 20° C. Duration ofetching 2 min Etching rate (top/sidewall) 0.3 nm/min, 2.4 nm/min

FIG. 11 illustrates a cross-sectional view of the silicon nitride films.Since RF power is 100 W which is lower than the threshold RF power(which is expected to be 600 W), a sidewall portion of the film isremoved selectively relative to a top portion 53 b of the film and abottom portion 53 a of the film by wet etching, wherein only thetop/bottom portions 53 a, 53 b remain after the wet etching. This filmcan be used as a cap layer.

Example 6

SiN films were deposited under the conditions shown in Table 8, wherethe threshold pressure was determined to be approximately 300 Pa in amanner substantially similar to that in Example 1. The SiN films werethen subjected to wet etching under the conditions shown in Table 8.FIG. 15 shows Scanning Transmission Electron Microscope (STEM)photographs of cross-sectional views of the silicon nitride films. Ascan be seen from FIG. 15, when the pressure was 150 Pa, the top/bottomportions of the film were selectively removed by wet etching, andsubstantially no film remained (no residual film was observed) on thetop surface and at the bottom of the trench. When the pressure was 250Pa, the top/bottom portions of the film were more predominantly removedthan was the sidewall portion of the film by wet etching, but residualfilm remained on the top surface and at the bottom of the trench,whereas the sidewall portion of the film mostly remained. When thepressure was 350 Pa, the sidewall portion of the film was morepredominantly removed than were the top/bottom portions of the film bywet etching, and no residual film remained in some areas of thesidewall, whereas the top/bottom portions of the film mostly remained.

TABLE 8 (numbers are approximate) Conditions for Deposition CycleSubstrate temperature 450° C. Bottle temperature  35° C. Showerheadtemperature 200° C. Wall temperature 150° C. Inflow gas temperature  75°C. Precursor SiI2H2 Variable (see FIG. 15) Pressure 350 Pa 250 Pa 150 PaReactant N₂ Flow rate of reactant 5000 sccm 2500 sccm (continuous) Flowrate of carrier gas 4000 sccm N₂ 2000 sccm N₂ (continuous) Flow rate ofseal gas 200 sccm N₂ (continuous) RF power (13.56 MHz) for a 990 W300-mm wafer Precursor pulse 0.45 sec Precursor purge 0.50 sec RF powerpulse 3.30 sec Purge 0.10 sec Growth rate per cycle (on 0.046 nm/ 0.018nm/ 0.028 nm/cycle top surface) cycle cycle Number of cycles (thickness500 times 265 times 500 times of film on top surface) (23.1 nm) (4.76nm) (14.2 nm) Step coverage (side/top; 79%; 88% 73%; 65% 78%; 75%side/bottom) Trench depth/width (nm) 330/33 (AR = about 10) Distancebetween electrodes 15 mm Conditions for Wet etching Etching solution1:100 DHF Etching solution temperature 20° C. Duration of etching 1 minEtching rate Variable (see FIG. 15)

Example 7

SiN films were deposited under the conditions shown in Table 9, wherethe threshold RF power (HRF alone) was determined to be approximately550 W in a manner substantially similar to that in Example 1. The SiNfilms were then subjected to wet etching under the conditions shown inTable 9. FIG. 16 shows Scanning Transmission Electron Microscope (STEM)photographs of cross-sectional views of the silicon nitride films. Ascan be seen from FIG. 16, when HRF power (13.56 MHz) was 880 W withoutLRF power, the top/bottom portions of the film were selectively removedby wet etching, and substantially no film remained (no residual film wasobserved) on the top surface and at the bottom of the trench. When HRFpower was 550 W without LRF power, the top/bottom portions of the filmand the sidewall portion of the film were about equally etched andmostly remained. When HRF power was 550 W and 50 W of LRF power (400kHz) was added thereto, the top/bottom portions of the film were morepredominantly removed than was the sidewall portion of the film by wetetching, and no residual film remained in some areas of the top/bottom,whereas the sidewall portion of the film mostly remained.

TABLE 9 (numbers are approximate) Conditions for Deposition CycleSubstrate temperature 450° C. Bottle temperature  35° C. Showerheadtemperature 200° C. Wall temperature 150° C. Inflow gas temperature  75°C. Precursor SiI₂H₂ Pressure Variable (see FIG. 16) Reactant N₂ Flowrate of reactant 5000 sccm (continuous) Flow rate of carrier gas 2000sccm N₂ (continuous) Flow rate of seal gas 200 sccm N₂ (continuous) RFpower (13.56 MHz) for 550 W 550 W 880 W a 300-mm wafer RF power (400kHz) for a 0 W (None) 50 W 0 W (None) 300-mm wafer Precursor pulse 0.30sec 0.30 sec 0.30 sec Precursor purge 1.00 sec 1.00 sec 0.5 sec RF powerpulse 3.30 sec 3.30 sec 3.30 sec Purge 0.10 sec 0.10 sec 0.10 sec Growthrate per cycle (on 0.038 nm/ 0.052 nm/ 0.045 nm/ top surface) cyclecycle cycle Number of cycles (thickness 300 times 300 times 430 times offilm on top surface) (11.3 nm) (15.5 nm) (19.6 nm) Step coverage(side/top; 73%; 68% 73%; 68% 67%; 77% side/bottom) Trench depth/width(nm) 100/33 (AR = about 3) Distance between electrodes 12 mm 12 mm 15 mmConditions for Wet etching Etching solution 1:100 DHF Etching solutiontemperature 20° C. Duration of etching 5 min Etching rate Variable (seeFIG. 16)

Example 8

SiN films were deposited under the conditions shown in Table 10, wherethe threshold RF power (HRF alone) was determined to be approximately400 W in a manner substantially similar to that in Example 1. The SiNfilms were then subjected to wet etching under the conditions shown inTable 10. FIG. 17 shows Scanning Transmission Electron Microscope (STEM)photographs of cross-sectional views of the silicon nitride films. Ascan be seen from FIG. 17, when HRF power (13.56 MHz) was 200-250 Wwithout LRF power, the sidewall portion of the film was selectivelyremoved by wet etching, and substantially no film remained (no residualfilm was observed) on the sidewall surface of the trench. When LRF power(430 kHz) was 300 W without HRF power, the top/bottom portions of thefilm were selectively removed by wet etching, and substantially no filmremained (no residual film was observed) on the top surface and at thebottom of the trench, whereas the sidewall portion of the film mostlyremained.

TABLE 10 (numbers are approximate) Conditions for Deposition Cycle HRFpower (13.56 MHz) for a 300-mm 200-250 W 0 W wafer LRF power (430 kHz)for a 300-mm wafer 0 W 300 W Substrate temperature 450° C. Pressure 10Torr 4 Torr Precursor DCS Reactant NH₃ Flow rate of reactant(continuous) 50 sccm Flow rate of carrier gas (continuous) 1,000 sccm ArFlow rate of dilution gas (continuous) 500 sccm N₂, 2,000 sccm ArPrecursor pulse 0.5 sec Precursor purge 1.0 sec Reactant pulse w/o RFplasma 0.5 sec RF power pulse 2.0 sec Purge 0.5 sec Growth rate percycle (on top surface) 0.73 Å/min > 0.73 Å/min Number of cycles(thickness of film on top 480 times (445 nm) surface) Step coverage(side/top; side/bottom) 70%; 70% Non-uniformity in film thickness within3.73% 0.86% wafer surface Trench depth/width (nm) 100/33 (AR = about 3)Distance between electrodes 10 mm Conditions for Wet etching Etchingsolution DI:HF = 100:1 Etching solution temperature Room temperatureDuration of etching >0.5 min Etching rate Variable (see FIG. 17)

Example 9

As shown in FIG. 17, by manipulating a ratio of HRF/LRF, reversetopological selectivity (RTS) can effectively be accomplished. Thereason that the top/bottom portions of the film were selectively removedby wet etching when the LRF power was used appears to reside in theamount of impurities such as hydrogen contained in the resultant film.It appears that the LRF power process generated more hydrogen radicalsthan did the HRF power process and provided more hydrogen atoms to thefilm, increasing the wet etch rate. Table 11 below shows the hydrogencontent of the SiN films deposited on the blanket (flat) wafer in thesame manner as in Example 8. As shown in Table 11, the SiN film formedby the LRF power process contained more hydrogen atoms than the SiN filmformed by the HRF power process, resulting in higher WER in the SiN filmby the LRF power process than that by the HRF power process.Accordingly, it can be understood that the hydrogen content in the filmis one of the main factors of the RTS.

TABLE 11 (numbers are approximate) WER Hydrogen content (at. %) tothermal oxide HRF (13.56 MHz, 200 W) 21.0 at. % 1.30 LRF (430 KHz, 300W) 26.2 at. % 6.31

Example 10 (Prophetic Example)

As shown in Example 2 (FIG. 8), by manipulating RF power (HRF), reversetopological selectivity (RTS) can effectively be accomplished. Also, asshown in FIG. 17, by manipulating a ratio of HRF/LRF, reversetopological selectivity (RTS) can effectively be accomplished. In thewet etching step following the deposition step, as an etching solution(etchant solution), not only a hydrogen fluoride (HF) but alsophosphoric acid (H₃PO₄) or any other suitable solution can be used foraccomplishing RTS. However, the type of etching solution can affect thedegree of RTS. For example, Table 12 shows that the etching rates at atop surface and at sidewalls of a trench vary depending on the type ofetchant solution, wherein the deposited dielectric film is formed in amanner similar to that in Example 2 or Example 8.

TABLE 12 (numbers are approximate) Etchant Top Side solution (nm/min)(nm/min) Film profile BHF130* 2 0.5 Similar to “700 W” in FIG. 8 or“LRF” in FIG. 17 0.2 5 Similar to “300 W” in FIG. 8 or “HRF” in FIG. 1770° C.-H₃PO₄ 4 0 Similar to “700 W” in FIG. 8 or “LRF” in FIG. 17 0.2 5Similar to “300 W” in FIG. 8 or “HRF” in FIG. 17 *Manufactured by DaikinIndustries, Ltd., Japan (a hydrogen fluoride containing 5% ammoniumhydrogen fluoride, 37% ammonium fluoride, and 58% water)

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

We/I claim:
 1. A method for fabricating a layer structure constituted bya dielectric film containing a Si—N bond in a recess formed in asubstrate, comprising: (i) simultaneously forming a dielectric filmcontaining a Si—N bond on an upper surface and a bottom surface and asidewall of the recess, wherein a top/bottom portion of the dielectricfilm formed on the upper surface and the bottom surface and a sidewallportion of the dielectric film formed on the sidewall are givendifferent chemical resistance properties by bombardment of a plasmaexcited by applying voltage in a reaction space between two electrodesbetween which the substrate is placed in parallel to the two electrodes;and (ii) substantially removing selectively the sidewall portion of thedielectric film among the top/bottom portion and the sidewall portion ofthe dielectric film by etching which removes the sidewall portion of thedielectric film more predominantly than the other according to thedifferent chemical resistance properties, wherein the plasma in step (i)is a capacitively coupled plasma (CCP) which is excited by applying RFpower to one of the two electrodes, wherein plasma density in step (i)is adjusted in a manner rendering the chemical resistance properties ofthe top/bottom portion of the dielectric film higher than the chemicalresistance properties of the sidewall portion of the dielectric film,and wherein the plasma density is modulable as a function of a ratio ofhigh frequency RF power to a total of high frequency RF power and lowfrequency RF power constituting the RF power, wherein the plasma densitydecreases when increasing the ratio, wherein in step (i), solely thehigh frequency RF power is used, and the ratio is one, wherein thehigh-frequency RF power has a frequency of 1 MHz or higher, and thelow-frequency RF power has a frequency of less than 1 MHz.
 2. The methodaccording to claim 1, wherein the plasma is a plasma of Ar, N₂, or O₂.3. The method according to claim 1, wherein in step (i), a halogenatedsilane is used as a precursor.
 4. The method according to claim 1,wherein the etching is the wet etching, which is conducted using asolution of hydrogen fluoride (HF) or phosphoric acid.